

LAW OF SPECIALIZATION OF PHYLETIC BRANCHES 213 



owing to their enormous dagger-shaped upper 

 canines, and to their three pairs of horns ranged on 

 the upper part of the cranium and increasing in 

 size from front to back. 



From the standpoint of the Darwinian hypo- 

 thesis it would be logical to attribute to the struggle 

 for life the survival of all these forms, either very 

 well adapted to their functions, or very well armed 

 for attack and defence ; and one might even be 

 brought to see in the struggle for life the funda- 

 mental cause of the progress of the specialization of 

 the organs in a given direction. It would, therefore, 

 seem a priori that the phyletic branches most cap- 

 able of preservation must be those whose mutations 

 most rapidly reached a great stature, an adaptation 

 perfect for their wants, and a powerful offensive 

 or defensive armament. We shall see, a little later, 

 when studying the causes of extinction in species, 

 that the problem is far from being so simple, and 

 that a too advanced degree of specialization, how- 

 ever useful it may seem to be to the animal possess- 

 ing it, is, on the other hand, generally a cause of 

 decline and of death. 



This is because the general law which drives 

 phyletic Branches to advance towards an ever- 

 increasing specialization of a few, at least, of their 

 structural features, does not always appear to be 

 clearly connected with the simple satisfaction of 

 functional needs, and with a better adaptation to 

 the environment. Consider, for instance, the 

 characteristics of evolution in the innumerable 

 branches of the Ammonites. One of the most 

 habitual phenomena of this evolution consists in a 



